BRENTWOOD, N.H. — Kathryn "Kat" McDonough, 19, of Portsmouth pleaded guilty Thursday to hindering the prosecution, conspiracy and witness tampering during her involvement with the alleged murder of 19-year-old University of New Hampshire student Elizabeth "Lizzi" Marriott. She was taken into custody at the conclusion of the hearing.

Ms. McDonough also pleaded guilty to "purposefully and repeatedly" lying to investigators about the disappearance of the UNH sophomore last fall.

She will serve 1½ to 3 years in a New Hampshire state prison and must comply with conditions including counseling and education programs, and having no contact with Ms. Marriott's family or ex-boyfriend Seth Mazzaglia.

Nine of Ms. Marriott's family members and her girlfriend were in Rockingham Superior Court Thursday to read impact statements.

Ms. McDonough lived with Mr. Mazzaglia at the time of Ms. Marriott's death. He is charged with strangling the 19-year-old Westboro marine biology student in October. The couple admitted to investigators that they dumped Ms. Marriott's body in the waters off Peirce Island in Portsmouth. The search for her body continues.

Rockingham Superior Court Judge Marguerite L. Wageling accepted Ms. McDonough's guilty pleas and sentenced her to 3½ to seven years consecutively for each charge. She will only serve 1½ to 3 years, however, with the rest suspended, said Assistant Attorney General Peter Hinckley, if she adheres to conditions including testifying in the first-degree murder trial against Mr. Mazzaglia.

Mr. Hinckley said his office hopes that trial will begin the first week of May 2014.

During the hearing, he said, Ms. McDonough repeatedly lied to police during the investigation, saying she and Mr. Mazzaglia hadn't seen Ms. Marriott the night she died and also asked friends who saw Ms. Marriott's lifeless body and blue face lying on the floor of her apartment to lie about it.

Ms. McDonough stood while Judge Wageling read the charges against her and made sure she fully understood she was waiving her rights to a trial.

Dressed in a pink dress covered by a short, gray sweater, wearing glasses and with short, curly black hair, Ms. McDonough sounded like a child as she softly responded "yes" over and over again to the judge's questions.

It was a stark comparison to the descriptions of Ms. McDonough in the victim witness statements delivered by Ms. Marriott's loved ones. Most wove the words "evil" and "betrayal" about Ms. McDonough into their statements and said they believed Ms. Marriott would still be alive if she were not led her to her death the night of Oct. 9 in Ms. McDonough's and Mr. Mazzaglia's Mill Street apartment in Dover.

One of the longest victim statements was delivered by a tearful Brittany Atwood — Ms. Marriott's friend. Ms. Atwood said she was speaking not as Ms. Marriott's best friend, but as her girlfriend.

"One day you wake up with the love of your life and the happiest in the universe and the next, with no warning, it all changes," Ms. Atwood said, sobbing.

She said when she found out Ms. Marriott was dead, everything was ripped away from her, including hope and love, and replaced with emptiness, darkness and hate.

"I will never forget her gorgeous eyes, cute dimples, contagious smile and bubbly personality," she said, and added about the times Ms. Marriott sang to her, "It was like everything in the world just stopped, froze for a while. It was just her and I."

Ms. Atwood said Ms. Marriott was her soulmate and she had never felt that much love or felt closer to anyone.

She and others said Ms. Marriott was too "good, sweet and pure" to see the "evil in Kat."

"I can never hold her hand, hug her, make her laugh or share special moments," she said. "It haunts me to know there was nothing I could do to save her — to stop it from happening. It has taken a toll on my mind, body and spirit. Kat is the reason my Lizzi is gone. It is all her fault. She could have prevented all this from happening."

She described Ms. McDonough as an evil actress with no feelings or emotions who acted cowardly and heartlessly and led Ms. Marriott to Mr. Mazzaglia. "He couldn't have done it without her help," she said. "If it wasn't for her, Lizzi would still be alive. No one should feel sorry for her … Lizzi will always be my girlfriend, hero and love of my life. I love you Lizzi with all my heart and I always will now and forever."

Ms. Atwood seemed almost inconsolable as Ms. Marriott's parents embraced her when she finished reading. Ms. Marriott's mother, Melissa Marriott, kept her arm around her through the rest of the hearing.

Other family members expressed their disappointment that New Hampshire does not have an accessory to murder law. They said they were not satisfied justice was served with Ms. McDonough's "soft" sentencing, but accepted it because it was the "right thing to do" to move the case against Mr. Mazzaglia forward.

Each said they were haunted with Ms. McDonough's inaction during Ms. Marriott's last moments — to try to stop Mr. Mazzaglia, call 911 or resuscitate her (though she had some first responder training.)

Mrs. Marriott said throwing the body into the water was "cruel and unusual punishment" because her daughter could not be brought home for a proper burial.

She called Ms. McDonough a "cold, calculating" woman who went on with her life for days after the alleged murder as if nothing was happening.

"I don't believe your portrayal as a victim," she said, in response to Ms. McDonough's claims that Mr. Mazzaglia was controlling and manipulative in their relationship.

She said Ms. McDonough owed Lizzi to start doing something positive with her life.

Each family member described living through depression and unimaginable grief since Ms. Marriott's death.

Her aunt Suzie Panneton-Bailey said she hoped Ms. McDonough would always be haunted by "Lizzi's pleas to save her life."

Ms. Marriott's uncle Tony Hanna, with whom she lived while attending college in New Hampshire, said his wife almost had a fatal heart attack following her niece's death, his 13-year-old daughter lost her innocence the day her cousin died and her son Joe Hanna, who is 10 days older than Ms. Marriott, harbors feelings of guilt for not being able to protect her.

"He would say to her, 'I'm 10 days older than you,' and Lizzi would say, 'Yah. That just means you'll die first,' " Mr. Hanna said. "Why did you let this happen? Why didn't you stop it? You couldn't have ran into the hall or pushed him away? You had no compassion for her as a woman."

Ms. Marriott's maternal and paternal grandmothers also delivered statements and other aunts and uncles, including her aunt Becky Tyning, with whom she lived when she was younger and volunteered at the New England Aquarium in Boston.

"I hold you personally responsible for Lizzi's death," she said. "If it wasn't for you, she'd still be here today… You just sat there and watched her die."

Her father, Robert Marriott, said the family accepted Ms. McDonough's pleas as the "right thing to do in the criminal case" to keep it moving forward, though it was not a fair or just sentence.

Though New Hampshire does not have a specific accessory to murder charge, it would have been "much more fitting," he said.

"Lizzi is gone forever and the defendant lives and will walk free in a short period of time," Mr. Marriott said. "Lizzi met Kat and thought she made a new friend and it got her killed … There are no words that can capture my grief and rage for what has happened …

"I want to say goodbye to a person when they die. That is something I'll never be able to do to my baby."